The present invention relates to an electronic apparatus such an an electronic cash register and a teller machine. The present invention relates, more particularly, to a program modification system for modifying a part of a program memorized in a program memory included in the electronic apparatus.
Generally, in an electronic apparatus such as an electronic cash register, a system control program is memorized in a mask ROM. When the program has been written into the mask ROM, it can not be changed and, therefore, the system operation program can not be changed or modified without exchanging the mask ROM.
Accordingly, an object of the present invention is to provide a program modification system for modifying a part of an operation program memorized in an electronic apparatus.
Another object of the present invention is to provide an electronic cash register, wherein a part of an operation program can be modified without exchanging a read only memory which stores the operation program.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an operation program is memorized in a mask ROM. A first RAM is provided which has the same addresses as the mask ROM in order to store information indicating whether the program of the respective address should be changed or not. A second RAM is provided for storing a modification program, the second RAM having addresses different from the mask ROM. A third RAM is provided for storing the mask ROM address of which program should be changed, and for storing the address of the second RAM which stores the modified operation program. The system operation is controlled by the operation program memorized in the mask ROM and the modification information stored in the first, second and third RAM's.
In a preferred form, a backup battery is provided for supplying power to the second and third RAM's in order to maintain the modification information even when the main power switch is switched off.